In recent years, carbon nanotubes having specific physical, chemical, and mechanical properties (hereinafter also referred to as CNT) have attracted attention. Particularly, since CNT aggregate comprising a plurality of CNTs aligned in an identical direction have a property different between the direction of orientation and the direction perpendicular thereto, that is, anisotropy with respect to electric properties (for example, electric conductivity), optical properties (for example, transmittance), and mechanical properties (for example, bending property), such aligned CNTs have a pronounced trend to be applied to devices for micro-machines (MEMS) or electronic devices. Particularly, in the aggregate of aligned CNTs, ions can easily diffuse among the aligned CNTs. Therefore, it is useful also as electrode materials for high power super capacitors.
For promoting the practical use of the aligned CNTs in the fields described above, it is important to improve the mass productivity of the aligned CNTs. The present inventors have found that an aligned CNT aggregate which is excellent in purity, specific surface area, and alignment and, in addition, increased remarkably in the size can be obtained by the presence of a small amount of water in a reaction atmosphere in the CNT growing method by a chemical vapor deposition method (hereinafter also referred to as a CVD method) when compared with the conventional method, and have reported the same in Non-Patent Document 1.
In addition, a technique of supplying water vapor together with a feedstock gas into a reaction container in the growing step of a vertically aligned CNT film has been proposed in Patent Document 1.    Non-Patent Document 1: Kenji Hata, et al., Water-Assisted Highly Efficient Synthesis of Impurity-Free Single-Walled Carbon Nanotubes, SCIENCE, 2004 Nov. 19, vol. 306, p. 1362-1364.    Patent Document 1: JP-A-2007-261839